This invention relates to economical upgrading of heavy oils, particularly heavy hydrocarbons, into lighter more valuable, more useful hydrocarbons. More specifically, this invention relates to a process of reacting emulsified heavy oil to form light oils, including naphtha and kerosene, plus other valuable organic products. This process is particularly well suited for use in upgrading heavy oil emulsified in water to valuable and commercially exploitable light hydrocarbons.
The total quantity of discovered heavy oil-in-place is estimated to be at least 4,500 billion barrels. By comparison, reserves of conventional oil are presently estimated to be about 700 billion barrels (recoverable). However, heavy crude oils, bitumen, tar sands, and shale oil are difficult to recover, transport and process economically, because they are exceptionally viscous. For example, heavy crude may be up to a million times more viscous than water. A solution to the problems presented by this high viscosity would provide the key to unlock massive world hydrocarbon resources.
Several methods have been suggested for the transportation of such crude by pipeline, however, emulsifying heavy crude and water has proven to be the most effective. Emulsifying the oil and water is effectively accomplished through a staged process. In the first stage, heavy oil and water containing low concentrations of a commercially available surfactant are mixed together. This process forms polyhedral shaped oil droplets separated by thin films of aqueous surfactant solution. In the second stage, diluent water is added to reduce the viscosity of the emulsion to the 50-100 mPa.s range. The emulsions contain oil droplets with a narrow, well-defined and controllable size range. This has advantages for both transportation (allows operators to meet pipeline viscosity specifications without adding expensive diluent, while maintaining stable emulsions during tanker and pipeline transportation) and combustion (as fuels for boilers and heaters).
These emulsions, represent an elegant solution to the problem of transporting viscous hydrocarbons. A useful state-of-the-art review of heavy oil/water emulsion technology is given in U.S. Pat. No. 4,776,977 herein incorporated by reference.
European Patent Application 0301766 teaches suitable uses for the emulsified oil and water emulsions. Emulsions of highly viscous fuel oils and water are frequently as much as 3-4 orders of magnitude less viscous than the oil itself and consequently are much easier to pump and require considerably less energy to do so. Furthermore, since the oil droplets are already in an atomized state, the emulsified fuel oil is suitable for use in low pressure burners and requires less preheating, resulting in savings in capital costs and energy. In addition, these fuel oil emulsions burn efficiently with low emissions of both particulate matter and NO.sub.x. This is an unusual and highly beneficial feature of the combustion.
Prior to the present invention, fuel combustion was the primary usage envisioned for the great quantity of oil/water emulsions available from high viscosity oil. However, to truly make the world's largest oil reserves (4,500 billion barrels of heavy oil) a valuable resource, an economically feasible means for directly treating the emulsified oil/water to obtain more valuable, more useful light hydrocarbons must be found.
Traditionally, heavy oil has been converted to lighter more valuable hydrocarbons through processes such as catalytic cracking, coking, and thermal cracking. These techniques, however, result in a great deal of highly refractory materials. Hydrocracking, has also been employed, however, the capital expenditures, due to the requirement of hydrogen plants, fuel, and feed for the production of hydrogen or a source of hydrogen are extremely high. Furthermore, all of these techniques have had extensive problems with contaminants often found in heavy oils, including NO.sub.x. These contaminants are both environmentally destructive and often ruin the catalysts used in traditional heavy crude oil upgrading processes.
An alternative technique for recovering relatively low boiling hydrocarbons from heavy oil is supercritical-fluid extraction (dense fluid extraction). The basic principals of supercritical-fluid extraction are outlined in the Kirk Othmer Encyclopedia of Chemical Technology, 3rd Edition, John Wiley & Sons, Supplemental Volume, pp. 872-893 (1984).
Dense fluid extraction occurs due to the strong effects of slight pressure and temperature changes upon a fluid solvent in its critical region resulting in extremely large changes in solvent density and therefore in its dissolving power. Close to its critical point, the density of a fluid is extremely sensitive to these changes, and as a result of density changes the solvent powers of the fluid fluctuate. Dense fluid extraction functions more effectively than the prior art technologies, because the excellent solubility of a solvent under supercritical pressures allows superb extraction and separation characteristics. Selective extraction occurs during exposure of the solvent to the solute, while separation occurs when the pressure is reduced and the solvent density returns to that of a gaseous state, allowing the solutes to separate from solution depending upon their volatility. Both the extraction stage and the separation stage can be controlled to obtain optimum separation. For example mild conditions (pressure and temperature) can be used to extract or separate highly volatile materials, and the conditions can be gradually increased in intensity to extract or separate less volatile materials.
In general, dense fluid extraction at elevated temperatures can be considered as a better alternative to distillation at high temperature because, the destruction of conventional cracking or coking reactions does not occur, and environmental conditions are improved.
A useful state-of-the-art review of dense phase upgrading of hydrocarbons is given in U.S. Pat. No. 3,948,754. In that patent, a process is disclosed for recovering hydrocarbons from oil shale or tar sand solids and simultaneously cracking, hydrogenating, desulfurizing, demetallizing, and denitrifying the recovered hydrocarbons. This process comprises contacting the oil shale or tar sands solids with a water containing fluid at a temperature from about 600.degree. F. to about 900.degree. F. at super-atmospheric pressure in the absence of externally supplied hydrogen. This process, however, does not solve the problem associated with transporting the heavy hydrocarbons, oil shale, or tar sand solids from the production site to a processing facility and thus requires the processing facility to be located at the production site. As discussed previously, the oil reserves of this nature are generally remotely located and building production sites at these remote locations is economically unacceptable. The method of the present invention incorporates emulsified transportation technology with a dense fluid processing system to provide a direct process for treating an emulsified oil feedstock to obtain higher valued light hydrocarbon products. Furthermore, the use of an emulsified oil feedstock of the present invention has been demonstrated to produce significantly better results in upgrading heavy oils in comparison to processes utilizing simple non-emulsified oil/solvent mixtures.